> Incidentally, why do we have _urdi_ 'of a man' but _vr.ta_ 'chosen' and
> _vr.ks.a_ 'tree'?
u:rdi does not mean "of a man". Monier-Williams lists it as "N. of a man",
which means "name of a man". It is the proper name of a particular
individual.
This, however, does not answer your basic question. A more interesting
souce for the same question is the root (1) vr. = "cover". It shows both
vr.noti and u:rnoti. The first is presumably from PIE *vl-ne-u-ti (Pokorny
page 1140). I don't know why the second has a long vowel, and reverses
syllabicity. Perhaps someone else can explain?
Peter